1. Field of the Invention
The present invention relates to a liquid crystal display and a method of manufacturing the same and, more particularly, to a vertical alignment type liquid crystal display in which liquid crystal molecules are aligned substantially perpendicularly to substrate surfaces when no voltage is applied and a method of manufacturing the same.
2. Description of the Related Art
Active matrix liquid crystal displays (LCDs) prevailing in the related art are TN (Twisted Nematic) mode liquid crystal displays in which a liquid crystal material having positive dielectric constant anisotropy is aligned in parallel with surfaces of substrates and is twisted 90° between the substrates that are provided opposite to each other. However, TN mode liquid crystal displays have the problem of low viewing angle characteristics, and various studies are therefore being made to improve the viewing angle characteristics of TN mode liquid crystal displays.
As an alternative to the TN mode, MVA (Multi-domain Vertical Alignment) type liquid crystal displays have been developed, in which a liquid crystal material having negative dielectric constant anisotropy is vertically aligned and in which the tilting direction of liquid crystal molecules at the time of application of a voltage is regulated using protrusions or slits provided on a surface of a substrate. A significant improvement of viewing angle characteristics is successfully achieved in MVA type liquid crystal displays.
A general MVA type liquid crystal display will now be described with reference to FIGS. 9A to 10. FIGS. 9A and 9B are conceptual illustrations of the MVA type liquid crystal display showing a section of the display taken in an oblique direction. FIG. 10 is a conceptual illustration showing a configuration of three pixels of the MVA type liquid crystal display and aligning directions of liquid crystal molecules therein. In the MVA type liquid crystal display, as shown in FIGS. 9A and 9B, liquid crystal molecules 108 of a liquid crystal material having negative dielectric constant anisotropy are aligned between two glass substrates 110 and 111 substantially perpendicularly to surfaces of the substrates. Although not shown, a pixel electrode connected to a thin film transistor (TFT) is formed at each pixel region on the glass substrate 110, and a common electrode is formed throughout a surface of the glass substrate 111. Protrusions 120 are formed on the pixel electrodes, and protrusions 121 are formed on the common electrode. The protrusions 120 and 121 are disposed such that they are alternately arranged. Vertical alignment films, which are not shown, are formed on the pixel electrodes, common electrodes, and protrusions 120 and 121.
When the TFT is off and no voltage is therefore applied to the liquid crystal molecules 108, the liquid crystal molecules 108 are aligned substantially perpendicularly to a substrate interface as shown in FIG. 9A. When the TFT is turned on, a predetermined voltage is applied to the liquid crystal molecules 108, and the tilting direction of the liquid crystal molecules 108 is regulated by the structure in which the protrusions 120 and 121 are formed. As a result, the liquid crystal molecules 108 are aligned in a plurality of directions as shown in FIG. 9B. For example, when the protrusions 120 and 121 are formed as shown in FIG. 10, the liquid crystal molecules 108 are aligned in four directions A, B, C, and D in one pixel. The MVA type liquid crystal display can achieve high viewing angle characteristics because the liquid crystal molecules 108 in one pixel are aligned in a plurality of directions when the TFT is turned on as thus described.
In the MVA type liquid crystal display, the tilting direction of the liquid crystal molecules 108 is not regulated by the alignment films. Therefore, the MVA method does not necessitate an aligning process such as rubbing that is essential for horizontal aligning methods represented by the TN mode. This is advantageous for processing in that the problem of static electricity and scraps generated by rubbing is eliminated and in that there is no need for a cleaning step after an aligning process. Another advantage accrues from the viewpoint of display quality in that there is no display irregularity attributable to variation of a pre-tilt. As described above, an MVA type liquid crystal display is characterized in that it can be provided at a low cost through simplification of manufacturing processes and an improvement of the yield of manufacture and in that high display quality can be achieved.
However, alignment films must be formed through coating even for MVA type liquid crystal displays for which rubbing is not required. As a result, the yield of manufacture is reduced by irregularities of the film thickness and entrapment of foreign substances that occur at an alignment film printing step, which increases material costs and tact time. As thus described, MVA type liquid crystal displays according to the related art still have the problem of an increase in manufacturing cost attributable to an alignment film printing step.
Recently, there is a trend toward very large mother glasses which accommodate larger liquid crystal displays. However, it is difficult to have alignment film printing apparatus follow up mother glasses which are becoming very large. Further, thin and soft film-like substrates and substrates having a curved shape rather than a planar shape have recently come into use. It is quite difficult to print an alignment film on such substrates. For this reason, a liquid crystal display utilizing a large mother glass or a substrate having a special shape has a problem in that it is difficult to achieve preferable liquid crystal alignment.    Patent Document 1: JP-A-11-95221    Patent Document 2: JP-A-5-249471